What do you do when the boss says he has a great idea, his mind is made up and have you any objections?

The above situation currently confronts the government's 87 top career personnel directors.

They are men and women who have reached the top of a very tough, important segment of the U.S. establishment by remembering the motto CYA (cover your assets).

Some of the personnel chiefs have half a million employes in their charge. Most of them have at some point felt the need to tell a temporary political master (an agency head or the president) that his or her desires were illegal, immoral or dumb.

A surprising number--not all--have stood up to the boss. Some who refused to fawn at the right time still have the bureaucratic scars to prove it.

The personnel people have until May 31 to point out any warts they can find on a job overhaul plan the president has embraced. There are four proposals that the administration hopes to have in place by the fall.

One would restrict overtime. Another would limit the areas and issues (already very limited) that unions and government agencies can negotiate.

The items that concern the most federal workers deal with reduction-in-force (RIF) rules and eligibility for in-grade pay increase.

Under the Reagan plan senior employes (who now enjoy the most layoff protection) could be RIFfed ahead of employes with less service who have better current job performance ratings.

Step promotions, which are now almost automatic based on time in grade, would be subject to good performance ratings. Employes in so-called career ladder jobs (which permit them to jump two pay grades every year) would have to get higher ratings to get promotions.

"A lot of things in the proposals are good, in fact most of them are good," one personnel director said. "The overtime thing, who cares? The union bargaining restriction is silly. But the performance-based incentive program is a sound concept. What we in the personnel community would like to do is convince them OPM and the White House to give us time to put this in place. The performance rating system from the CSRA civil service retirement act still isn't functioning properly." But the personnel director said he would be cautious in making comments. "I get the impression they want cheers, not criticism. We can make technical points but not oppose anything substantive."

Another personnel director said a colleague "got into trouble" with the secretary of his department for "saying some unkind things about the RIF regulations. You think we won't be cautious after that?"

Criticism of the plan is "out," one personnel director said. "I think we all got the impression at the April Fool's Day meeting at OPM it was held on April 1 , and last Thursday that our comments are to be limited to technical matters. Of course a lot of important things can be brought up as technical matters."

Of a dozen personnel directors interviewed, only one said that he did not feel "any restraints on any comments we care to make on the regs. I'll talk to my boss and let him know what I think we should say."

Several of the personnel directors said they would be happier with the PBIS (performance-based incentive system) if an employe's chances of being RIFfed or getting an in-grade promotion were not pegged to his last performance rating.

"You can't take a single picture of somebody's performance and make a decision based on that picture," said one personnel chief. "If we can convince them to consider the employe's work history--say three performance ratings--it would sit better with a lot of people."

Administration officials hope to have the two major reforms--RIFs and in-grade pay raises--in place by early fall. If they take the personnel community's educated suggestions seriously, they might get a system that is not only good, but that also works.